Carbon catalyst, method of producing same, and electrode and battery each utilizing same

ABSTRACT

Provided is a method of producing a carbon catalyst having an improved activity. The method of producing carbon catalyst including a carbonization step of carbonizing raw materials containing an organic compound as a carbon source, a metal, and an electrically conductive carbon material to produce a carbonized material; a metal impregnation step of impregnating the carbonized material with a metal; and a heat treatment step of subjecting the carbonized material impregnated with the metal to a heat treatment.

This is a Division of application Ser. No. 13/505,068 filed Apr. 30,2012, which in turn is a National Stage of International Application No.PCT/JP2010/069567 filed Nov. 4, 2010, which claims priority to JapaneseApplication No. 2009-254057 filed Nov. 5, 2009. The disclosures of theprior applications are hereby incorporated by reference herein in theirentireties.

TECHNICAL FIELD

The present invention relates to a carbon catalyst, a method ofproducing a carbon catalyst, and an electrode and a battery each usingthe carbon catalyst, and more particularly, to an improvement in anactivity of a carbon catalyst.

BACKGROUND ART

A platinum catalyst is currently used in a number of chemical reactionsand next-generation batteries. However, there still remain many problemsto be solved as described below. For example, in a polymer electrolytefuel cell (PEFC), the use of platinum results in an increased cost, andreserves of platinum are limited. In addition, in an air cell, the useof platinum results in an increased cost in the same manner as describedabove, and a chemical reaction such as decomposition of an electrolytesolution is caused by platinum. Therefore, the use of platinum is amajor obstacle to widespread adoption of the next-generation batteries.

In view of the foregoing, for example, a carbon catalyst as described inPatent Literature 1 has been developed as an alternative catalyst toplatinum.

PRIOR ART DOCUMENT Patent Document

-   -   [Patent Document 1] JP 2008-282725 A

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, a fuel cell using the conventional carbon catalyst hasinsufficient performance compared to one using the platinum catalyst.

The present invention has been made in view of the problems. An objectof the present invention is to provide a carbon catalyst having animproved activity, a method of producing a carbon catalyst, and anelectrode and a battery each using the carbon catalyst.

Means for Solving the Problems

In a carbon catalyst according to an embodiment of the present inventionfor achieving the object, the total of a desorption amount of carbonmonoxide and a desorption amount of carbon dioxide in a temperatureprogrammed desorption method from 150° C. to 400° C. is 0.06 mmol ormore per 0.02 g. According to the present invention, there is provided acarbon catalyst having an improved activity.

In addition, the desorption amount of carbon monoxide may be 0.01 mmolor more and the desorption amount of carbon dioxide may be 0.05 mmol ormore.

A carbon catalyst according to an embodiment of the present inventionfor achieving the object is obtained by: carbonizing raw materialscontaining an organic compound as a carbon source, a metal, and anelectrically conductive carbon material to produce a carbonizedmaterial; impregnating the carbonized material with a metal; andsubjecting the carbonized material with the metal to a heat treatment.According to the present invention, there is provided a carbon catalysthaving an improved activity.

An electrode according to an embodiment of the present invention forachieving the object includes any one of the carbon catalysts. Accordingto the present invention, there is provided an electrode including acarbon catalyst having an improved activity.

A battery according to an embodiment of the present invention forachieving the object includes the electrode. According to the presentinvention, there is provided a battery including an electrode includinga carbon catalyst having an improved activity.

A method of producing a carbon catalyst according to an embodiment ofthe present invention for achieving the object includes: a carbonizationstep of carbonizing raw materials containing an organic compound as acarbon source, a metal, and an electrically conductive carbon materialto produce a carbonized material; a metal impregnation step ofimpregnating the carbonized material with a metal; and a heat treatmentstep of subjecting the carbonized material impregnated with the metal toa heat treatment. According to the present invention, there is provideda method of producing a carbon catalyst having an improved activity.

In addition, the metal impregnation step may include impregnating thecarbonized material with a metal of a kind different from the metal inthe raw materials. In addition, the heat treatment step may includeheating the carbonized material at 300° C. or more.

A carbon catalyst according to an embodiment of the present inventionfor achieving the object is produced by any one of the methods.According to the present invention, there is provided a carbon catalysthaving an improved activity.

Effect of the Invention

According to the present invention, a carbon catalyst having an improvedactivity, a method of producing a carbon catalyst, and an electrode anda battery each using the carbon catalyst are provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory diagram illustrating main steps in an exampleof a method of producing a carbon catalyst according to an embodiment ofthe present invention.

FIG. 2 is an explanatory diagram illustrating an example of results ofevaluation of characteristics of a carbon catalyst in an embodiment ofthe present invention.

FIG. 3 is an explanatory diagram illustrating an example of results ofevaluation of a carbon catalyst by a temperature programmed desorptionmethod in an embodiment of the present invention.

FIG. 4 is an explanatory diagram illustrating an example of results ofevaluation of a carbon structure of a carbon catalyst in an embodimentof the present invention.

FIG. 5 is an explanatory diagram illustrating an example of results ofevaluation of an oxygen reduction activity of a carbon catalyst in anembodiment of the present invention.

FIG. 6 is an explanatory diagram illustrating an example of results ofevaluation of a four-electron reduction reaction rate of an oxygenreduction reaction with a carbon catalyst in an embodiment of thepresent invention.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the present invention is described. Itshould be noted that the present invention is not limited to an exampledescribed in this embodiment.

First, a method of producing a carbon catalyst according to thisembodiment (hereinafter, referred to as “production method of thepresent invention”) is described. FIG. 1 is an explanatory diagramillustrating main steps in an example of the production method of thepresent invention. As illustrated in FIG. 1, the production method ofthe present invention includes a carbonization step S1, a metalimpregnation step S2, and a heat treatment step S3.

In the carbonization step S1, raw materials containing an organiccompound as a carbon source, a metal, and an electrically conductivecarbon material are carbonized so that a carbonized material isobtained. The organic compound in the raw materials is not particularlylimited as long as the compound is carbonized, and one or two or morekinds of arbitrary compounds may be used. That is, one or both of ahigh-molecular weight organic compound (e.g., a resin such as athermoplastic resin or a thermosetting resin) and a low-molecular weightorganic compound may be used as the organic compound, and biomass mayalso be used.

In addition, for example, an organic compound containing nitrogen may bepreferably used as the organic compound. The organic compound containingnitrogen is not particularly limited as long as the compound contains anitrogen atom in a molecule thereof, and one or two or more kinds ofarbitrary compounds may be used.

In addition, for example, a ligand that coordinates to a metal may bepreferably used as the organic compound. That is, in this case, anorganic compound containing one or more ligand atoms in a moleculethereof is used. More specifically, for example, an organic compoundcontaining, as a ligand atom, one or two or more kinds selected from thegroup consisting of a nitrogen atom, phosphorus atom, an oxygen atom,and a sulfur atom in a molecule thereof may be used. For example, anorganic compound containing, as a ligand group, one or two or more kindsselected from the group consisting of an amino group, a phosphino group,a carboxyl group, and a thiol group in a molecule thereof may also beused.

Specifically, for example, one or two or more kinds selected from thegroup consisting of pyrrole, vinylpyridine, imidazole,2-methylimidazole, aniline, a polysulfone, a polyaminobismaleimide, apolyimide, a polyvinyl alcohol, a polybenzoimidazole, a polyimide, apolyether, a polyetheretherketone, cellulose, lignin, chitin, chitosan,silk, wool, a polyamino acid, a nucleic acid, DNA, RNA, hydrazine,hydrazide, urea, an ionomer, a polyacrylic acid, a polyacrylic acidester, a polymethacrylic acid ester, a polymethacrylic acid, a phenolresin, a melamine resin, an epoxy resin, a furan resin, a polyamideimideresin, and a polyacrylonitrile may be used as the organic compound.

The organic compound may further contain, for example, one or two ormore kinds selected from the group consisting of boron, phosphorus,oxygen, and sulfur as a component for improving the activity of thecarbon catalyst to be produced by the production method of the presentinvention.

The metal in the raw materials is not particularly limited as long asthe metal does not inhibit the activity of the carbon catalyst to beproduced by the production method of the present invention, and one ortwo or more kinds of arbitrary metals may be used. The metal may be, forexample, one or two or more kinds selected from the group consisting ofGroups 3 to 16 of the periodic table. That is, one or two or more kindsselected from the group consisting of Group 3A (Group 3) element, Group4A (Group 4) element, Group 5A (Group 5) element, Group 6A (Group 6)element, Group 7A (Group 7) element, Group 8 (Groups 8, 9, and 10)element, Group 1B (Group 11) element, Group 2B (Group 12) element, Group3B (Group 13) element, Group 4B (Group 14) element, Group 5B (Group 15)element, and Group 6B (Group 16) element of the periodic table may beused.

In addition, for example, a transition metal (belonging to Groups 3 to12 of the periodic table) may be preferably used as the metal. Inaddition, a metal belonging to the fourth period of Groups 3 to 12 ofthe periodic table may be preferably used as the transition metal.

Specifically, for example, one or two or more kinds selected from thegroup consisting of scandium (Sc), titanium (Ti), vanadium (V), chromium(Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu),zinc (Zn), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo),ruthenium (Ru), rhodium (Rh), palladium (Pd), lanthanoids (e.g., cerium(Ce)), and actinoids may be preferably used, and one or two or morekinds selected from the group consisting of manganese, iron, cobalt,nickel, and copper may be more preferably used.

The metal may be used as the simple substance of the metal or a compoundof the metal. For example, a metal salt, a metal oxide, a metalhydroxide, a metal nitride, a metal sulfide, a metal carbide, or a metalcomplex may be used as the metal compound. Of those, a metal salt, ametal oxide, a metal sulfide, or a metal complex may be preferably used.It should be noted that when a ligand is used as the organic compound, ametal complex is to be formed in the raw materials.

The electrically conductive carbon material in the raw materials is notparticularly limited as long as the material imparts electricalconductivity to the carbon catalyst to be produced by the productionmethod of the present invention or improves the electrical conductivityof the carbon catalyst, and one or two or more kinds of arbitrarymaterials may be used. That is, for example, a carbon material that haselectrical conductivity but does not have any catalytic activity byitself may be used as the electrically conductive carbon material.

Specifically, for example, one or two or more kinds selected from thegroup consisting of carbon black, carbon nanotube, carbon nanohorn,carbon fiber, carbon fibril, and a graphite powder may be used.

The use of each of those electrically conductive carbon materials mayincrease the contact area at the three-phase interface of a carbonstructure of a carbonized material to improve the activity of the carboncatalyst to be produced by the production method of the presentinvention, for example.

Electrically conductive carbon material that has been caused to carrythe metal in the raw materials in advance may also be used. That is, inthis case, for example, an electrically conductive carbon materialcarrying a transition metal that improves the activity or oxidationresistance of the carbon catalyst may be used. As the transition metal,for example, one or two or more kinds selected from the group consistingof scandium, titanium, vanadium, chromium, manganese, iron, cobalt,nickel, copper, zinc, yttrium, zirconium, niobium, molybdenum,ruthenium, rhodium, palladium, lanthanoids (e.g., cerium), and actinoidsmay be used.

In the carbonization step S1, prior to the carbonization, the rawmaterials containing such organic compound, metal, and electricallyconductive carbon material as described above are mixed. A method ofmixing the raw materials is not particularly limited, and for example, amortar or a stirring apparatus may be used. One or two or more kinds ofmixing methods such as powder mixing involving mixing the organiccompound, the metal, and the electrically conductive carbon material inpowdery states, and solvent mixing involving adding and mixing, asolvent may also be employed.

Then, in the carbonization step S1, the raw materials prepared asdescribed above are carbonized. That is, the raw materials are heatedand held at such a predetermined temperature that the raw materials arecarbonized (carbonization temperature).

The carbonization temperature is not particularly limited as long as theraw materials are carbonized at the temperature, and for example, thetemperature may be 300° C. or more. More specifically, for example, thecarbonization temperature may be 300° C. or more and 1,500° C. or less,may be preferably 400° C. or more and 1,200° C. or less, and may be morepreferably 500° C. or more and 1,100° C. or less.

A rate of temperature increase upon heating of the raw materials to thecarbonization temperature is not particularly limited and may be, forexample, 0.5° C./min or more and 300° C./min or less. The time periodfor which the raw materials are held at the carbonization temperature(carbonization time) is not particularly limited as long as the rawmaterials are carbonized within the time period, and for example, thetime may be 5 minutes or more. More specifically, for example, thecarbonization time may be 5 minutes or more and 240 minutes or less, andmay be preferably 20 minutes or more and 180 minutes or less. Inaddition, the carbonization is preferably performed in an inert gas suchas nitrogen (e.g., in a flow of the inert gas).

Thus, in the carbonization step S1, the carbonized material produced bythe carbonization of the raw materials is obtained. It should be notedthat the resultant carbonized material may be pulverized. A method ofpulverizing the carbonized material is not particularly limited, and forexample, a pulverizing apparatus such as a ball mill or a bead mill maybe used. For example, the average particle diameter of the carbonizedmaterial after the pulverization may be 150 μm or less, and may bepreferably 45 μm or less. In consideration of an application to amembrane electrode assembly (MEA), the average particle diameter of thecarbonized material is preferably as small as possible.

In the subsequent metal impregnation step S2, the carbonized materialobtained in the carbonization step S1 is impregnated with a metal. Themetal with which the carbonized material is impregnated is notparticularly limited as long as the metal does not inhibit the activityof the carbon catalyst to be produced by the production method of thepresent invention, and one or two or more kinds of arbitrary metals maybe used.

The metal may be, for example, one or two or more kinds selected fromthe group consisting of Groups 3 to 16 of the periodic table. Inaddition, for example, a transition metal (belonging to Groups 3 to 12of the periodic table) may be preferably used as the metal. Further, ametal belonging to the fourth period, fifth period, or sixth period ofGroups 3 to 12 of the periodic table may be preferably used as thetransition metal.

Specifically, for example, one or two or more kinds selected from thegroup consisting of titanium, chromium, manganese, iron, cobalt, nickel,copper, zinc, zirconium, niobium, molybdenum, ruthenium, lanthanum,cerium, and tantalum may be preferably used, and one or two or morekinds selected from the group consisting of titanium, iron, zirconium,ruthenium, and cerium may be more preferably used.

In addition, in the metal impregnation step S2, the carbonized materialmay be impregnated with a metal of a kind different from the metal inthe raw materials used in the carbonization step S1. That is, forexample, the carbonized material may be impregnated with one or two ormore kinds selected from the group consisting of aluminum, silicon,titanium, chromium, manganese, iron, cobalt, nickel, copper, zinc,gallium, zirconium, niobium, molybdenum, ruthenium, indium, tin,lanthanum, cerium, tantalum, and lead or from the group consisting oftitanium, iron, zirconium, ruthenium, and cerium, and different from themetal in the raw materials.

The metal may be used as the simple substance of the metal or a compoundof the metal. For example, a metal salt, a metal oxide, a metalhydroxide, a metal nitride, a metal sulfide, a metal carbide, or a metalcomplex may be used as the metal compound. Of those, a metal salt, ametal oxide, a metal sulfide, or a metal complex may be preferably used.

A method of impregnating the carbonized material with the metal in themetal impregnation step S2 is not particularly limited as long as atleast the surface of the carbonized material is impregnated with themetal, and for example, a method involving bringing the carbonizedmaterial into contact with a solution containing the metal may beemployed.

That is, the carbonized material may be impregnated with the metal by,for example, immersing and holding the carbonized material in ametal-containing solution. In this case, the carbonized material may beheld in the boiling metal-containing solution. In addition, an acidicsolution may be used as the metal-containing solution. In this case, thepH of the metal-containing solution may be, for example, 1 or more and 6or less.

In the subsequent heat treatment step S3, the carbonized material thathas been impregnated with the metal in the metal impregnation step S2 issubjected to a heat treatment. The heat treatment is performed byholding the carbonized material at a predetermined temperature (heattreatment temperature).

That is, in the heat treatment step S3, the carbonized material isheated at, for example, 300° C. or more. The heat treatment temperaturemay be, for example, 400° C. or more. More specifically, for example,the heat treatment temperature may be 300° C. or more and 1,500° C. orless, may be preferably 400° C. or more and 1,400° C. or less, and maybe more preferably 500° C. or more and 1,300° C. or less.

The heat treatment temperature may be the same temperature as thecarbonization temperature, or may be a temperature different from thecarbonization temperature. That is, for example, the heat treatmenttemperature may be a temperature equal to or lower than thecarbonization temperature of the raw materials in the carbonization stepS1, or may be a temperature lower than the carbonization temperature.Alternatively, the heat treatment temperature may be a temperaturehigher than the carbonization temperature.

Specifically, for example, when the carbonization temperature in thecarbonization step S1 is 400° C. or more and 1,100° C. or less, the heattreatment temperature may be a temperature that is 300° C. or more and1,000° C. or less, and is equal to or lower than the carbonizationtemperature or is lower than the carbonization temperature.

A rate of temperature increase upon heating of the carbonized materialto the heat treatment temperature is not particularly limited and maybe, for example, 0.5° C./min or more and 300° C./min or less. The timeperiod for which the carbonized material is held at the heat treatmenttemperature (heat treatment time) is not particularly limited as long asan effect of the heat treatment is obtained within the time, and forexample, the time may be 5 minutes or more. More specifically, forexample, the heat treatment time may be 5 minutes or more and 240minutes or less, and may be preferably 20 minutes or more and 180minutes or less. In addition, the heat treatment is preferably performedin an inert gas such as nitrogen (e.g., in a flow of the inert gas).

Thus, in the heat treatment step S3, the carbonized material subjectedto the heat treatment after the impregnation with the metal is obtained.It should be noted that the resultant carbonized material may bepulverized. A method of pulverizing the carbonized material is notparticularly limited, and for example, a pulverizing apparatus such as aball mill or a bead mill may be used. For example, the average particlediameter of the carbonized material after the pulverization may be 150μm or less, and may be preferably 45 μm or less. In consideration of anapplication to a membrane electrode assembly, the average particlediameter of the carbonized material is preferably as small as possible.

It should be noted that in the production method of the presentinvention, nitrogen atoms or boron atoms may also be introduced (doped)into the carbonized material in an arbitrary step. That is, for example,nitrogen atoms or boron atoms may be introduced into the carbonizedmaterial obtained in the carbonization step S1, the carbonized materialafter the metal impregnation obtained in the metal impregnation step S2,and/or the carbonized material after the heat treatment obtained in theheat treatment step S3. For example, a vapor phase doping method such asan ammoxidation method or a CVD method, a liquid phase doping method, ora vapor phase-liquid phase doping method may be employed as a method ofintroducing nitrogen atoms or boron atoms. Specifically, for example, anitrogen atom may be introduced into the surface of the carbonizedmaterial by: mixing a nitrogen source such as ammonia, melamine, oracetonitrile or a boron source such as boric acid or sodium borohydridewith the carbonized material; and holding the resultant mixture in anatmosphere of an inert gas such as nitrogen, argon, or helium at atemperature of 550° C. or more and 1,200° C. or less for a time periodof 5 minutes or more and 180 minutes or less. In addition, the resultantcarbonized material may be subjected to an activating treatment such ascarbon dioxide activation, phosphoric acid activation, alkaliactivation, hydrogen activation, ammonia activation, activation withnitrogen oxide, or electrolytic activation and/or liquid phase oxidationsuch as nitric acid oxidation, mixed acid oxidation, or hydrogenperoxide oxidation.

In the production method of the present invention, the carbonizedmaterial obtained in the heat treatment step S3 may be obtained as acarbon catalyst. According to the production method of the presentinvention including the carbonization step S1, the metal impregnationstep S2, and the heat treatment step S3 as described above, a carboncatalyst having an improved activity compared with a conventional one isproduced. That is, the production method of the present inventioneffectively improves the activity of the carbon catalyst by including,in particular, the metal impregnation step S2 and the heat treatmentstep S3.

Although a carbonized material having a catalytic activity is obtainedin the carbonization step S1 in the production method of the presentinvention, the catalytic activity is significantly improved by furthersubjecting the carbonized material to a metal impregnation treatment anda heat treatment.

The mechanism via which the activity of the carbon catalyst is improvedby the metal impregnation treatment and the heat treatment may be, forexample, that a new carbon structure different from a carbon structureformed by the carbonization is formed by the metal impregnationtreatment and the heat treatment.

It should be noted that while the metal in the raw materials may beplaced not only on the surface of the carbonized material but also inthe entirety of the inside thereof while being dispersed therein, themetal with which the carbonized material has been impregnated in themetal impregnation step S2 is locally placed mainly on the surface ofthe carbonized material and a vicinity thereof.

Therefore, it may be said that the metal impregnation treatment and theheat treatment each have an aspect of a surface treatment for thecarbonized material. In terms of the foregoing as well, the carbonstructure formed by the metal impregnation treatment and the heattreatment may be different from the carbon structure formed by thecarbonization.

In addition, in the production method of the present invention, atreatment for removing a metal in the carbonized material (metal removaltreatment) may be performed as required (for example, when the metalbecomes unnecessary after the carbonization).

That is, the production method of the present invention may furtherinclude: a metal removal step of subjecting the carbonized materialsubjected to the heat treatment in the heat treatment step S3 to a metalremoval treatment; and an after-metal removal heat treatment step ofsubjecting the carbonized material subjected to the metal removaltreatment to a heat treatment.

The metal removal treatment is not particularly limited as long as ametal in the carbonized material is removed or the amount of the metalis reduced by the treatment, and for example, a washing treatment withan acid or an electrolytic treatment may be performed.

The acid to be used in the acid washing is not particularly limited aslong as an effect of the metal removal treatment is obtained, and one ortwo or more kinds of arbitrary acids may be used. That is, for example,one or two or more kinds selected from the group consisting ofhydrochloric acid (such as concentrated hydrochloric acid), nitric acid(such as concentrated nitric acid), and sulfuric acid (such asconcentrated sulfuric acid) may be used. When two or more kinds of acidsare used, for example, a mixed acid prepared by mixing concentratedhydrochloric acid and concentrated nitric acid at a predetermined volumeratio (such as aqua regia), or a mixed acid prepared by mixingconcentrated nitric acid and concentrated sulfuric acid at apredetermined volume ratio may be used.

The acid washing method is not particularly limited as long as theeffect of the metal removal treatment is obtained, and for example, amethod involving immersing and holding the carbonized material in asolution containing an acid may be employed. In this case, thecarbonized material may be held in the boiling acid solution.

In the subsequent after-metal removal heat treatment step, the same heattreatment as the heat treatment in the heat treatment step S3 isperformed. Thus, in the after-metal removal heat treatment step, acarbonized material subjected to the heat treatment after the metalremoval is obtained. It should be noted that the resultant carbonizedmaterial may be pulverized as in the carbonized material subjected tothe heat treatment in the heat treatment step S3.

In addition, in the production method of the present invention, thecarbonized material obtained in the after-metal removal heat treatmentstep may be obtained as a carbon catalyst. A carbon catalyst having anadditionally improved activity is produced by performing such metalremoval treatment and after-metal removal heat treatment. That is, inthis case, the activity of the carbon catalyst is effectively improvedby, for example, removing a metal component from the carbonized materialto expose an active site.

It should be noted that in the production method of the presentinvention, the metal impregnation treatment may be performed in themetal impregnation step S2 after the carbonized material obtained in thecarbonization step S1 has been subjected to such metal removal treatmentas described above. That is, in this case, in the metal impregnationstep S2, the carbonized material from which the metal in the rawmaterials has been removed is impregnated with the metal. Alternatively,the metal impregnation treatment may be performed without subjecting thecarbonized material to the metal removal treatment. That is, in thiscase, in the metal impregnation step S2, the carbonized material isimpregnated with the metal without the removal of the metal in the rawmaterials from the carbonized material.

Alternatively, the production method of the present invention mayfurther include: an additional metal impregnation step of furtherimpregnating the carbonized material subjected to the heat treatment inthe heat treatment step S3 with a metal; and an additional heattreatment step of subjecting the carbonized material impregnated withthe metal in the additional metal impregnation step to a heat treatment.That is, the production method of the present invention includes, forexample, the carbonization step S1, the metal impregnation step S2, theheat treatment step S3, the additional metal impregnation step, and theadditional heat treatment step.

In the additional metal impregnation step, the metal with which thecarbonized material is impregnated is not particularly limited as longas the metal does not inhibit the activity of the carbon catalyst to beproduced by the production method of the present invention, and one ortwo or more kinds of arbitrary metals may be used.

The metal may be, for example, one or two or more kinds selected fromthe group consisting of Groups 3 to 16 of the periodic table. Inaddition, for example, a transition metal (belonging to Groups 3 to 12of the periodic table) may be preferably used as the metal. Further, ametal belonging to the fourth period, fifth period, or sixth period ofGroups 3 to 12 of the periodic table may be preferably used as thetransition metal.

Specifically, for example, one or two or more kinds selected from thegroup consisting of titanium, chromium, manganese, iron, cobalt, nickel,copper, zinc, zirconium, niobium, molybdenum, ruthenium, lanthanum,cerium, and tantalum may be preferably used, and one or two or morekinds selected from the group consisting of titanium, iron, zirconium,ruthenium, and cerium may be more preferably used.

In addition, in the additional metal impregnation step, the carbonizedmaterial may be impregnated with a different kind of metal from themetal in the raw materials used in the carbonization step S1. That is,for example, the carbonized material may be impregnated with one or twoor more kinds selected from the group consisting of aluminum, silicon,titanium, chromium, manganese, iron, cobalt, nickel, copper, zinc,gallium, zirconium, niobium, molybdenum, ruthenium, indium, tin,lanthanum, cerium, tantalum, and lead or from the group consisting oftitanium, iron, zirconium, ruthenium, and cerium, and different from themetal in the raw materials.

In addition, in the additional metal impregnation step, the carbonizedmaterial may be impregnated with a different kind of metal from themetal with which the material has been impregnated in the metalimpregnation step S2. That is, for example, the carbonized material maybe impregnated with one or two or more kinds selected from the groupconsisting of aluminum, silicon, titanium, chromium, manganese, iron,cobalt, nickel, copper, zinc, gallium, zirconium, niobium, molybdenum,ruthenium, indium, tin, lanthanum, cerium, tantalum, and lead, or fromthe group consisting of titanium, iron, zirconium, ruthenium, andcerium, and different from the metal with which the carbonized materialhas been impregnated in the metal impregnation step S2. In addition, inthe additional metal impregnation step, the carbonized material may beimpregnated with a different kind of metal from the metal with which thematerial has been impregnated in the metal impregnation step S2, themetal being capable of having a valence of 4. That is, in this case, forexample, the carbonized material is impregnated with a divalent ortrivalent metal in the metal impregnation step S2, and then thecarbonized material is impregnated with a tetravalent metal in theadditional metal impregnation step.

The metal may be used as the simple substance of the metal or a compoundof the metal. For example, a metal salt, a metal oxide, a metalhydroxide, a metal nitride, a metal sulfide, a metal carbide, or a metalcomplex may be used as the metal compound. Of those, a metal salt, ametal oxide, a metal sulfide, or a metal complex may be preferably used.

A method of impregnating the carbonized material with the metal in theadditional metal impregnation step is not particularly limited as longas at least the surface of the carbonized material is impregnated withthe metal, and for example, a method involving bringing the carbonizedmaterial into contact with a solution containing the metal may beemployed.

That is, the carbonized material may be impregnated with the metal by,for example, immersing and holding the carbonized material in ametal-containing solution. In this case, the carbonized material may beheld in the boiling metal-containing solution. In addition, an acidicsolution may be used as the metal-containing solution. In this case, thepH of the metal-containing solution may be, for example, 1 or more and 6or less.

In the subsequent additional heat treatment step, the same heattreatment as the heat treatment in the heat treatment step S3 isperformed. It should be noted that a heat treatment temperature in theadditional heat treatment step may be the same temperature as the heattreatment temperature in the heat treatment step S3, or may be atemperature different from the heat treatment temperature.

Thus, in the additional heat treatment step, a carbonized materialsubjected to the heat treatment after the additional metal impregnationtreatment is obtained. It should be noted that the resultant carbonizedmaterial may be pulverized as in the carbonized material subjected tothe heat treatment in the heat treatment step S3. In addition, in theproduction method of the present invention, the additional metalimpregnation step and the additional heat treatment step may each berepeated twice or more.

In addition, in the production method of the present invention, thecarbonized material obtained in the additional heat treatment step maybe obtained as a carbon catalyst. A carbon catalyst with an additionallyimproved activity is produced by performing such additional metalimpregnation treatment and additional heat treatment. That is, in thiscase, the activity of the carbon catalyst is effectively improved by,for example, further forming a new carbon structure.

Alternatively, the production method of the present invention mayfurther include the additional metal impregnation step and theadditional heat treatment step, and the metal removal step and theafter-metal removal heat treatment step. That is, the production methodof the present invention includes, for example, the carbonization stepS1, the metal impregnation step S2, the heat treatment step S3, themetal removal step, the after-metal removal heat treatment step, theadditional metal impregnation step, and the additional heat treatmentstep.

In this case, in the additional metal impregnation step, the carbonizedmaterial subjected to the metal removal treatment and the after-metalremoval heat treatment after the heat treatment in the heat treatmentstep S3 is impregnated with a metal again. When the additional metalimpregnation step and the additional heat treatment step are eachrepeated twice or more, the carbonized material after the heat treatmentin each additional heat treatment step may be subjected to a metalremoval treatment and an after-metal removal heat treatment.

Alternatively, the production method of the present invention mayfurther include: an acid treatment step of subjecting the carbonizedmaterial subjected to the heat treatment in the heat treatment step S3to an acid treatment; and an after-acid treatment heat treatment step ofsubjecting the carbonized material subjected to the acid treatment to aheat treatment. That is, the production method of the present inventionincludes, for example, the carbonization step S1, the metal impregnationstep S2, the heat treatment step S3, the acid treatment step, and theafter-acid treatment heat treatment step.

An acid to be used in the acid treatment is not particularly limited aslong as an effect of the acid treatment is obtained, and one or two ormore kinds of arbitrary acids may be used. That is, for example, one ortwo or more kinds selected from the group consisting of hydrochloricacid (such as concentrated hydrochloric acid), nitric acid (such asconcentrated nitric acid), and sulfuric acid (such as concentratedsulfuric acid) may be used. When two or more kinds of acids are used,for example, a mixed acid prepared by mixing concentrated hydrochloricacid and concentrated nitric acid at a predetermined volume ratio (suchas aqua regia), or a mixed acid prepared by mixing concentrated nitricacid and concentrated sulfuric acid at a predetermined volume ratio, maybe used.

A method for the acid treatment is not particularly limited as long asthe effect of the acid treatment is obtained, and for example, a methodinvolving immersing and holding the carbonized material in a solutioncontaining an acid may be employed. In this case, the carbonizedmaterial may be held in the boiling acid solution. It should be notedthat the carbonized material may be subjected to an acid treatment bywashing the carbonized material with an acid in the metal removal step.That is, the acid washing for metal removal may be a mode of the acidtreatment as a surface treatment.

In the subsequent after-acid treatment heat treatment step, the sameheat treatment as the heat treatment in the heat treatment step S3 isperformed. Thus, in the after-acid treatment heat treatment step, acarbonized material subjected to the heat treatment after the acidtreatment is obtained. It should be noted that the resultant carbonizedmaterial may be pulverized as in the carbonized material subjected tothe heat treatment in the heat treatment step S3. In addition, in theproduction method of the present invention, the acid treatment step andthe after-acid treatment heat treatment step may each be repeated twiceor more.

In addition, in the production method of the present invention, thecarbonized material obtained in the after-acid treatment heat treatmentstep may be obtained as a carbon catalyst. A carbon catalyst having anadditionally improved activity is produced by performing such acidtreatment and after-acid treatment heat treatment. That is, in thiscase, the activity of the carbon catalyst is effectively improved by,for example, introducing a new functional group on the surface of thecarbonized material and a vicinity thereof.

Alternatively, the production method of the present invention mayfurther include the acid treatment step and the after-acid treatmentheat treatment step, and the metal removal step and the after-metalremoval heat treatment step. That is, the production method of thepresent invention includes, for example, the carbonization step S1, themetal impregnation step S2, the heat treatment step S3, the metalremoval step, the after-metal removal heat treatment step, the acidtreatment step, and the after-acid treatment heat treatment step.

In this case, in the acid treatment step, the carbonized materialsubjected to the metal removal treatment and the after-metal removalheat treatment after the heat treatment in the heat treatment step S3 issubjected to an acid treatment. When the acid treatment step and theafter-acid treatment heat treatment step are each repeated twice ormore, the carbonized material after the heat treatment in eachafter-acid treatment heat treatment step may be subjected to a metalremoval treatment and an after-metal removal heat treatment.

Next, a carbon catalyst according to this embodiment (hereinafter,referred to as “catalyst of the present invention”) is described. Theinventors of the present invention have carried out extensiveinvestigations on a carbon structure for realizing a carbon catalysthaving a high activity on their own, in tandem with the method ofproducing a carbon catalyst as described above. As a result, theinventors have made an invention according to the catalyst of thepresent invention.

The catalyst of the present invention is, for example, such a carboncatalyst that the total of the desorption amount of carbon monoxide andthe desorption amount of carbon dioxide in a temperature programmeddesorption method from 150° C. to 400° C. is 0.06 mmol or more per 0.02g. That is, when 0.02 g of the catalyst of the present invention isevaluated by the temperature programmed desorption method, the totalamount of carbon monoxide and carbon dioxide to desorb during theheating of the catalyst of the present invention from 150° C. to 400° C.is 0.06 mmol or more.

In this case, the catalyst of the present invention may be, for example,such a carbon catalyst that in the temperature programmed desorptionmethod from 150° C. to 400° C., the desorption amount of carbon monoxideis 0.01 mmol or more and the desorption amount of carbon dioxide is 0.05mmol or more.

In addition, the total of the desorption amount of carbon monoxide andthe desorption amount of carbon dioxide in the temperature programmeddesorption method from 150° C. to 400° C. may be, for example, 0.07 mmolor more. In this case, for example, the desorption amount of carbonmonoxide and the desorption amount of carbon dioxide may be 0.01 mmol ormore and 0.06 mmol or more, respectively.

In addition, the catalyst of the present invention is, for example, sucha carbon catalyst that the total of the desorption amount of carbonmonoxide and the desorption amount of carbon dioxide in the temperatureprogrammed desorption method from 150° C. to 900° C. is 0.4 mmol or moreper 0.02 g. In this case, the catalyst of the present invention may be,for example, such a carbon catalyst that in the temperature programmeddesorption method from 150° C. to 900° C., the desorption amount ofcarbon monoxide is 0.3 mmol or more and the desorption amount of carbondioxide is 0.1 mmol or more.

In addition, the total of the desorption amount of carbon monoxide andthe desorption amount of carbon dioxide in the temperature programmeddesorption method from 150° C. to 900° C. may be, for example, 0.46 mmolor more per 0.02 g. In this case, for example, the desorption amount ofcarbon monoxide and the desorption amount of carbon dioxide may be 0.33mmol, or more and 0.13 mmol or more, respectively.

The desorption amounts of carbon monoxide and carbon dioxide in thetemperature programmed desorption method are determined by a knownmethod. That is, first, a carbon catalyst is subjected to a heattreatment in a predetermined temperature programmed desorption apparatusso that a functional group (oxygen-containing compound) is desorbed fromthe surface of the carbon catalyst. Next, oxygen gas is brought intocontact with the carbon catalyst subjected to the heat treatment so thatthe surface of the carbon catalyst is caused to chemically adsorboxygen. After that, the carbon catalyst is subjected to a heat treatmentagain, and then the amounts of carbon monoxide and carbon dioxide to begenerated in association with the desorption of the functional group(oxygen-containing compound) from the surface of the carbon catalyst aredetermined.

The desorption amount of carbon monoxide and the desorption amount ofcarbon dioxide in the temperature programmed desorption method from 150°C. to 400° C. or 900° C. are determined as the total amounts of carbonmonoxide and carbon dioxide that have desorbed during a periodcommencing on the heating of a carbon catalyst to 150° C. and ending onsuch further heating of the carbon catalyst that its temperatureincreases to 400° C. or 900° C., respectively.

Such a temperature programmed desorption method is employed in theevaluation of a carbon material for its active surface area (ASA). Thatis, a carbon atom (edge carbon) on a carbon network surface in a carboncatalyst has been proved to be chemically active because the carbon atomhas an unsaturated sp² electron.

The edge carbon is quantified by measuring the adsorption amount of anoxygen atom to the edge carbon, and the resultant quantity is an activesurface area, which is regarded as a measure of the catalytic reactivityof the carbon catalyst. The temperature programmed desorption method isemployed as a method of determining the active surface area.

As oxygen more easily adsorbs to an edge surface in the carbon catalystthan to its basal surface, the amount of the edge surface of the carboncatalyst is indirectly determined by: causing the carbon catalyst fromwhich a surface functional group has been removed by heating at hightemperatures to adsorb oxygen; heating the carbon catalyst again afterthe adsorption; and determining the release amounts (desorption amounts)of carbon monoxide and carbon dioxide. Therefore, increases in thedesorption amounts of carbon monoxide and carbon dioxide measured by thetemperature programmed desorption method represent an increase in theactive surface area of the carbon catalyst, and also represent anincrease in the catalytic activity of the carbon catalyst.

As a result of their extensive investigations, the inventors of thepresent invention have found on their own that the activity of a carboncatalyst is improved compared with a conventional one when the carboncatalyst has a carbon structure in which such desorption of carbonmonoxide and carbon dioxide as described above occurs in the temperatureprogrammed desorption method.

The catalyst of the present invention has larger desorption amounts ofcarbon monoxide and carbon dioxide measured by the temperatureprogrammed desorption method than a conventional carbon catalyst does.Accordingly, it is considered that the catalyst of the present inventioncontains a large amount of edge surfaces, each having a large activesurface area and high reactivity, and as a result, shows a highercatalytic activity than the conventional carbon catalyst does.

In addition, the catalyst of the present invention is, for example, acarbon catalyst obtained by carbonizing raw materials containing anorganic compound as a carbon source, a metal, and an electricallyconductive carbon material to produce a carbonized material,impregnating the carbonized material with a metal, and subjecting thecarbonized material with the metal to a heat treatment.

In this case, the catalyst of the present invention may be preferablyproduced by the production method of the present invention as describedabove. That is, the catalyst of the present invention may be, forexample, a carbon catalyst produced by the production method of thepresent invention including the carbonization step S1, the metalimpregnation step S2, and the heat treatment step S3. In addition, thecatalyst of the present invention in this case may be a carbon catalysthaving a carbon structure in which such desorption of carbon monoxideand carbon dioxide as described above occurs in the temperatureprogrammed desorption method.

For example, the specific surface area of the catalyst of the presentinvention measured by a nitrogen adsorption BET method may be 10 m²/g ormore, and may be preferably 100 m²/g or more. More specifically, forexample, the specific surface area of the catalyst of the presentinvention may be 200 m²/g or more and 3,000 m²/g or less, and may bepreferably 300 m²/g or more and 3,000 m²/g or less.

The catalyst of the present invention has a catalytic activity such asan oxygen reduction activity. That is, the catalyst of the presentinvention effectively catalyzes an oxygen reduction reaction in anelectrode for a fuel cell, for example.

The oxygen reduction activity may be evaluated, for example, with anoxygen reduction-starting potential. The oxygen reduction-startingpotential may be determined, for example, based on data showing arelationship between a voltage and a current density obtained bypotential sweep application with a rotating ring-disk electrodeapparatus including a working electrode having applied thereto thecatalyst of the present invention (oxygen reduction voltammogram).

In addition, the oxygen reduction-starting potential of the catalyst ofthe present invention may be, for example, 0.785 V vs. NHE (vs. a normalhydrogen electrode) or more and 1.2 V vs. NHE or less, and may bepreferably 0.790 V vs. NHE or more and 1.2 V vs. NHE or less whenevaluated in terms of a voltage (E₀₂) at which a reduction current of−10 μA/cm² flows.

In addition, the catalytic activity of the catalyst of the presentinvention may be evaluated, for example, with the number of electronsinvolved in a reaction in an oxygen reduction reaction. The number ofelectrons involved in a reaction is calculated as the number ofelectrons involved in a reduction reaction for one molecule of oxygen inan oxygen reduction reaction to be catalyzed by the catalyst of thepresent invention.

That is, for example, in such a reaction that water is produced fromprotons and oxygen in a cathode (air electrode) of a fuel cell, fourelectrons are involved in a reduction reaction for one molecule ofoxygen, in theory. In actuality, however, such a reaction that twoelectrons are involved in a reduction reaction for one molecule ofoxygen to produce hydrogen peroxide also occurs in parallel. Thus, inthe oxygen reduction reaction of the cathode, it is said that the numberof electrons involved in the reduction reaction for one molecule ofoxygen is preferably closer to 4 because a current is extracted in alarger amount, hydrogen peroxide is suppressed from being produced, andan environmental load and deterioration in a power generation apparatusis also reduced.

In this regard, according to the catalyst of the present invention, thenumber of electrons involved in a reaction in an oxygen reductionreaction may be 3.5 or more and 4 or less, may be preferably 3.6 ormore, and may be more preferably 3.8 or more.

The catalyst of the present invention is a carbon catalyst having anexcellent activity as described above, and hence is used as analternative to an expensive platinum catalyst. That is, the catalyst ofthe present invention is formed of a carbonized material which not onlyhas a high activity by itself without carrying any platinum catalyst butis also inexpensive and has a high practical value.

Thus, the catalyst of the present invention is utilized as, for example,a synthesis catalyst, an environmental catalyst, an electrode catalystfor a battery, an electrode catalyst for a fuel cell, an electrodecatalyst for an air cell, or a hydrogen peroxide decomposition catalyst.According to the catalyst of the present invention, a variety ofchemical reactions such as an oxygen reduction reaction are effectivelypromoted without the use of any platinum catalyst.

An electrode according to this embodiment (hereinafter, referred to as“electrode of the present invention”) is an electrode including thecatalyst of the present invention. That is, the electrode of the presentinvention is, for example, an electrode carrying the catalyst of thepresent invention. Specifically, the electrode of the present inventionis, for example, an electrode including a predetermined electrode basematerial and the catalyst of the present invention carried by theelectrode base material.

The electrode of the present invention may be, for example, an electrodefor a fuel cell, and may be preferably an electrode for a polymerelectrolyte fuel cell (PEFC). In addition, the electrode of the presentinvention may be, for example, an electrode for an air cell. When theelectrode of the present invention is an electrode for a fuel cell or anelectrode for an air cell, the electrode of the present invention ispreferably a cathode.

That is, the catalyst of the present invention may be, for example, anelectrode catalyst for a fuel cell, and may be preferably an electrodecatalyst for a PEFC. In addition, the catalyst of the present inventionmay be, for example, an electrode catalyst for an air cell. Further,when the catalyst of the present invention is an electrode catalyst fora fuel cell or an electrode catalyst for an air cell, the catalyst ofthe present invention is preferably a cathode catalyst.

A battery according to this embodiment (hereinafter, referred to as“battery of the present invention”) is a battery including the electrodeof the present invention. That is, the battery of the present inventionis a battery including the electrode of the present invention as one, orboth, of a cathode and an anode.

The battery of the present invention may be, for example, a fuel cell,and may be preferably a PEFC. That is, the battery of the presentinvention may be, for example, a PEFC including a membrane electrodeassembly including the electrode of the present invention. In addition,the battery of the present invention may be, for example, an air cell.

Specifically, the battery of the present invention may be, for example,a PEFC including a membrane electrode assembly of a polymer electrolytemembrane integrated with a cathode (positive electrode or air electrode)and an anode (negative electrode or fuel electrode) respectively formedon one side and the other side of the polymer electrolyte membrane, andincluding the electrode of the present invention as one, or both, of thecathode and the anode. In this case, the battery of the presentinvention preferably includes the electrode of the present invention atleast as the cathode.

In addition, the battery of the present invention may be, for example, afuel cell having an open circuit voltage (OCV) equal to or more than apredetermined value. That is, the battery of the present invention maybe, for example, a fuel cell having an open circuit voltage of 0.78 V ormore. Further, the open circuit voltage of the battery of the presentinvention may be, for example, 0.80 V or more, may be preferably 0.85 Vor more, and may be more preferably 0.90 V or more.

In addition, the battery of the present invention may be a fuel cellhaving a voltage at a current density of 0.2 A/cm² (0.2-A voltage) of,for example, 0.59 V or more, preferably 0.60 V or more.

Next, a specific example according to this embodiment is described.

EXAMPLES Example 1 Production of Carbon Catalyst PCoFe

First, a raw material as an object to be carbonized was prepared. Thatis, 1.5 g of a polyacrylonitrile-polymethacrylic acid copolymer(PAN/PMA) was dissolved in 30 mL of dimethylformamide. After that, 1.5 gof 2-methylimidazole and 1.5 g of cobalt chloride hexahydrate(CoCl₂.6H₂O) were added to the solution, and then the mixture wasstirred at room temperature for 2 hours. Ketjen black (ECP600JDmanufactured by Lion Corporation) was added to the mixture thus obtainedso as to account for 30 wt % of the solid content to be incorporatedinto the raw material, and then the contents were mixed with a mortar.The resultant mixture was vacuum-dried at 60° C. for 12 hours.

Further, the mixture was heated in the atmosphere so that itstemperature was increased from room temperature to 150° C. in 30minutes. Subsequently, the temperature was increased from 150° C. to220° C. over 2 hours. After that, the mixture was held at 220° C. for 3hours so that the mixture was made infusible. Thus, the raw material fora carbonized material was prepared.

Next, the carbonization of the raw material was performed. That is, theraw material subjected to the infusible treatment as described above wasloaded into a quartz tube and subjected to nitrogen purge in an imagefurnace for 20 minutes, and then its temperature was increased from roomtemperature to 900° C. by heating over 18 minutes. After that, the rawmaterial was held at 900° C. for 1 hour so as to be carbonized. Thus, acarbonized material was obtained.

Further, the carbonized material was pulverized. That is, zirconia ballseach having a diameter of 10 mm were set in a planetary ball mill (P-7manufactured by FRITSCH JAPAN CO., LTD.), and then a treatment forpulverizing the carbonized material with the planetary ball mill for 5minutes at a rotational speed of 650 rpm was performed over 10 cycles.After that, the pulverized carbonized material was taken out and passedthrough a sieve having an aperture of 106 μm. The carbonized materialthat had passed through the sieve was obtained as a pulverized, fineparticulate carbonized material.

Next, a metal impregnation treatment was performed. That is, a solutionprepared by adding 2 g of iron (III) chloride hexahydrate (FeCl₃.6H₂O)to 300 mL of distilled water was boiled, and then 2 g of the carbonizedmaterial was added to the iron-containing solution. Then, the carbonizedmaterial was impregnated with iron for 3 hours while being stirred inthe iron-containing solution that was boiling. After that, the solutioncontaining the carbonized material was filtered with a membrane filter(having a pore diameter of 1.0 μm and manufactured by Millipore), andthen the filtrate was washed with distilled water until the filtratebecame neutral. The recovered carbonized material was vacuum-dried at60° C. for 12 hours. Further, the dried carbonized material waspulverized with a mortar.

Next, a heat treatment was performed. That is, the carbonized materialsubjected to the metal impregnation treatment as described above wasloaded into a quartz tube and subjected to nitrogen purge in an imagefurnace for 20 minutes, and then its temperature was increased from roomtemperature to 700° C. by heating over 14 minutes. After that, thecarbonized material was held at 700° C. for 1 hour.

Further, the carbonized material after the heat treatment waspulverized. That is, zirconia balls each having a diameter of 10 mm wereset in a planetary ball mill, and then a treatment for pulverizing thecarbonized material with the planetary ball mill for 5 minutes at arotational speed of 450 rpm was performed over 4 cycles. After that, thepulverized carbonized material was taken out and passed through a sievehaving an aperture of 106 μm. The carbonized material that had passedthrough the sieve was obtained as a pulverized, fine particulate carboncatalyst (PCoFe).

Example 2 Production of Carbon Catalyst PCoZr

A pulverized, fine particulate carbon catalyst (PCoZr) was obtained inthe same manner as in Example 1 above except that zirconium chlorideoxide octahydrate (ZrCl₂O.8H₂O) was used instead of iron(III) chloridehexahydrate (FeCl₃.6H₂O) in the metal impregnation treatment.

Example 3 Production of Carbon Catalyst PCoFeAw

The carbon catalyst (PCoFe) obtained in Example 1 above was subjected toa metal removal treatment by acid washing.

That is, 100 mL of concentrated hydrochloric acid was added to 1 g ofthe carbon catalyst (PCoFe), and then the mixture was stirred for 1hour. After the carbon catalyst had been precipitated and the solutionhad been removed, 100 mL of a solution prepared by mixing concentratedhydrochloric acid and distilled water at 1:1 (volume ratio) was added tothe carbon catalyst, and then the mixture was stirred for 1 hour. Afterthe carbon catalyst had been precipitated and the solution had beenremoved, 100 mL of distilled water was added to the carbon catalyst, andthen the mixture was stirred for 1 hour. The solution containing thecarbon catalyst was filtered with a membrane filter (having a porediameter of 1.0 μm and manufactured by Millipore), and then the filtratewas washed with distilled water until the filtrate became neutral. Therecovered carbon catalyst was vacuum-dried at 60° C. for 12 hours.Further, the dried carbon catalyst was pulverized with a mortar.

Next, an after-metal removal heat treatment was performed. That is, thecarbon catalyst subjected to the metal removal treatment as describedabove was loaded into a quartz tube and subjected to nitrogen purge inan image furnace for 20 minutes, and then its temperature was increasedfrom room temperature to 700° C. by heating over 14 minutes. After that,the carbon catalyst was held at 700° C. for 1 hour.

Further, the carbon catalyst after the heat treatment was pulverized.That is, zirconia balls each having a diameter of 10 mm were set in aplanetary ball mill, and then a treatment for pulverizing the carbonizedmaterial with the planetary ball mill for 5 minutes at a rotationalspeed of 450 rpm was performed 4 cycles. After that, the pulverizedcarbonized material was taken out and passed through a sieve having anaperture of 106 μm. The carbonized material that had passed through thesieve was obtained as a pulverized, fine particulate carbon catalyst(PCoFeAW).

Example 4 Production of Carbon Catalyst CoFeAW

A carbon catalyst (CoFeAW) was produced in the same manner as in Example3 above except that the following raw material free of PAN/PMA was usedas the raw material for a carbonized material.

That is, 1.5 g of 2-methylimidazole and 1.5 g of cobalt chloridehexahydrate (CoCl₂.6H₂O) were added to 30 mL of dimethylformamide, andthen the mixture was stirred at room temperature for 2 hours. Ketjenblack (ECP600JD, Lion Corporation) was added to the mixture thusobtained so as to account for 43 wt % of the solid content to beincorporated into the raw material, and then the contents were mixedwith a mortar. The resultant mixture was vacuum-dried at 60° C. for 12hours. The dried mixture was subjected to the same heating treatment asthat in Example 1 above so that the raw material for a carbonizedmaterial was prepared. Then, the subsequent procedure was performed inthe same manner as in Example 3 above. Thus, a pulverized, fineparticulate carbon catalyst (CoFeAW) was obtained.

Example 5 Production of Carbon Catalyst PCoFe(II)AW

A pulverized, fine particulate carbon catalyst (PCoFe(II)AW) wasobtained in the same manner as in Example 3 above except that iron(II)chloride tetrahydrate (FeCl₂.4H₂O) was used instead of iron(III)chloride in the metal impregnation treatment.

Example 6 Production of Carbon Catalyst PCoFeAWFe

The carbon catalyst (PCoFeAW) obtained in Example 3 above was subjectedto an additional metal impregnation treatment. That is, a solutionprepared by adding 2 g of iron (III) chloride hexahydrate (FeCl₃.6H₂O)to 300 mL of distilled water was boiled, and then 2 g of the carboncatalyst (PCoFeAW) was added to the iron-containing solution. Then, thecarbon catalyst was impregnated with iron for 3 hours while beingstirred in the iron-containing solution that was boiling. After that,the solution containing the carbon catalyst was filtered with a membranefilter (having a pore diameter of 1.0 μm and manufactured by Millipore),and then the filtrate was washed with distilled water until the filtratebecame neutral. The recovered carbon catalyst was vacuum-dried at 60° C.for 12 hours. Further, the dried carbon catalyst was pulverized with amortar.

Next, an additional heat treatment was performed. That is, the carboncatalyst subjected to the additional metal impregnation treatment asdescribed above was loaded into a quartz tube and subjected to nitrogenpurge in an image furnace for 20 minutes, and then its temperature wasincreased from room temperature to 700° C. by heating over 14 minutes.After that, the carbon catalyst was held at 700° C. for 1 hour.

Further, the carbon catalyst after the heat treatment was pulverized.That is, zirconia balls each having a diameter of 10 mm were set in aplanetary ball mill, and then a treatment for pulverizing the carboncatalyst with the planetary ball mill for 5 minutes at a rotationalspeed of 450 rpm was performed over 4 cycles. After that, the pulverizedcarbon catalyst was taken out and passed through a sieve having anaperture of 106 μm. The carbon catalyst that had passed through thesieve was obtained as a pulverized, fine particulate carbon catalyst(PCoFeAWFe).

Example 7 Production of Carbon Catalyst PCoFeAWZr

A pulverized, fine particulate carbon catalyst (PCoFeAWZr) was obtainedin the same manner as in Example 6 above except that zirconium chlorideoxide octahydrate (ZrCl₂O.8H₂O) was used instead of iron(III) chloridehexahydrate (FeCl₃.6H₂O) in the additional metal impregnation treatment.

Example 8 Production of Carbon Catalyst PCoFeAWTi

A pulverized, fine particulate carbon catalyst (PCoFeAWTi) was obtainedin the same manner as in Example 6 above except that a titanium(III)chloride solution (TiCl₃) was used instead of iron (III) chloridehexahydrate (FeCl₃.6H₂O) in the additional metal impregnation treatment.

Examples 9 Production of Carbon Catalyst PCoFeAWCe

A pulverized, fine particulate carbon catalyst (PCoFeAWCe) was obtainedin the same manner as in Example 6 above except that cerium chlorideheptahydrate (CeCl₃.7H₂O) was used instead of iron (III) chloridehexahydrate (FeCl₃.6H₂O) in the additional metal impregnation treatment.

Example 10 Preparation of Carbon Catalyst PCoFeAWHNO₃

The carbon catalyst (PCoFeAW) obtained in Example 3 above was subjectedto an acid treatment. That is, 100 mL of concentrated nitric acid wasadded to 1 g of the carbon catalyst (PCoFeAW) and the mixture wasstirred for 3 hours at normal temperature. After that, the solutioncontaining the carbon catalyst was filtered with a membrane filter(having a pore diameter of 1.0 μm and manufactured by Millipore), andthen the filtrate was washed with distilled water until the filtratebecame neutral. The recovered carbon catalyst was vacuum-dried at 60° C.for 12 hours. Further, the dried carbon catalyst was pulverized with amortar.

Next, an after-acid treatment heat treatment was performed. That is, thecarbon catalyst subjected to the acid treatment as described above wasloaded into a quartz tube and subjected to nitrogen purge in an imagefurnace for 20 minutes, and then its temperature was increased from roomtemperature to 700° C. by heating over 14 minutes. After that, thecarbon catalyst was held at 700° C. for 1 hour.

Further, the carbon catalyst after the heat treatment was pulverized.That is, zirconia balls each having a diameter of 10 mm were set in aplanetary ball mill, and then a treatment for pulverizing the carboncatalyst with the planetary ball mill for 5 minutes at a rotationalspeed of 450 rpm was performed over 4 cycles. After that, the pulverizedcarbon catalyst was taken out and passed through a sieve having anaperture of 106 μm. The carbon catalyst that had passed through thesieve was obtained as a pulverized, fine particulate carbon catalyst(PCoFeAWHNO₃).

Example 11 Production of Carbon Catalyst PCoFeAWR

A pulverized, fine particulate carbon catalyst (PCoFeAWR) was obtainedin the same manner as in Example 10 above except that aqua regia (mixedacid prepared by mixing concentrated hydrochloric acid and concentratednitric acid at a volume ratio of 3:1) was used instead of concentratednitric acid in the acid treatment.

Example 12 Production of Carbon Catalyst PCoFeAWNH₃

A nitrogen atom was doped into the carbon catalyst (PCoFe) obtained inExample 1 above by subjecting the carbon catalyst to the same metalremoval treatment by acid washing as that in Example 3 above andsubjecting the carbon catalyst after the metal removal treatment to aheat treatment in an ammonia (NH₃) gas atmosphere.

That is, in the same manner as in Example 3 above, the carbon catalystsubjected to the metal removal treatment was loaded into a quartz tubeand subjected to nitrogen purge in an image furnace for 20 minutes, andthen its temperature was increased from room temperature to 800° C. byheating over 16 minutes. Then, the nitrogen gas atmosphere was changedto an ammonia gas atmosphere, and the carbon catalyst was held under theammonia gas atmosphere at 800° C. for 30 minutes. Next, the ammonia gasatmosphere was changed to a nitrogen gas atmosphere again, and thecarbon catalyst was held under the nitrogen gas atmosphere at 800° C.for 20 minutes. After that, the image furnace was left to stand to coolto room temperature. Further, the carbon catalyst after the nitrogendoping was pulverized in the same manner as in Example 3 above. Thus, apulverized, fine particulate carbon catalyst (PCoFeAWNH₃) was obtained.

Comparative Example 1 Production of Carbon Catalyst PCoAW

A pulverized, fine particulate carbon catalyst (PCoAW) was obtained inthe same manner as in Example 3 above except that none of the metalimpregnation treatment, the heat treatment, and the pulverizationtreatment after the heat treatment were performed.

Comparative Example 2 Production of Carbon Catalyst PCoHNO₃

A pulverized, fine particulate carbon catalyst (PCoHNO₃) was obtained inthe same manner as in Example 3 above except that none of the metalimpregnation treatment, the heat treatment, and the pulverizationtreatment after the heat treatment were performed, and concentratednitric acid was used instead of concentrated hydrochloric acid in theacid treatment.

Comparative Example 3 Preparation of Ketjen Black

Ketjen black (ECP600JD, Lion Corporation) as an electrically conducivecarbon material was prepared as a carbonized material according toComparative Example 3.

Comparative Example 4 Preparation of Carbon Material Carrying Platinum

A carbon material carrying platinum (Pt/C) obtained by causing ketjenblack as a carrier to carry platinum at 40 wt % was prepared as acatalyst according to Comparative Example 4.

[Evaluation of Power Generation Performance, Oxygen Reduction Activity,and Number of Electrons Involved in Reaction in Fuel Cell]

First, a catalyst slurry containing any one of the carbon catalystsproduced in Examples 1 to 12 and Comparative Examples 1 and 2 above wasprepared. That is, 350 μL of a commercially available 5-wt % Nafion®solution (manufactured by Aldrich), 200 μL of ethanol, and 200 μL ofdistilled water were added to 0.1 g of the carbon catalyst, and thecontents were mixed with a mortar. The resultant mixture wasultrasonicated for 1 hour. Thus, a catalyst slurry was obtained.

Then, a cathode for a fuel cell (cathode catalyst layer) carrying thecarbon catalyst was produced. That is, the catalyst slurry was printedon a gas diffusion layer (manufactured by Toray Industries, Inc.) in twodivided portions with a commercially available coater and dried at 60°C. for 3 hours. Thus, a cathode catalyst layer was obtained. The size ofthe cathode catalyst layer was 2.3 cm×2.3 cm. The amount of the carboncatalyst carried in the resultant cathode catalyst layer was 3 mg/cm².

Next, a membrane electrode assembly (MEA) including the carbon catalystwas produced. That is, the cathode catalyst layer, a solid polymerelectrolyte membrane (Nafion® NRE212), and an anode catalyst layer(commercially available gas diffusion layer with carbon carryingplatinum at 0.5 wt %) were stacked in this order and hot-pressed at 150°C. and 0.4 MPa for 3 minutes. Thus, an MEA was obtained.

Further, a fuel cell including the MEA was produced. That is, the MEAobtained as described above was sandwiched with a separator. Thus, afuel cell was produced.

Then, the MEA including the carbon catalyst was evaluated for its powergeneration performance as described below. That is, hydrogen (80° C., arelative humidity of 100%) and oxygen (80° C., air having a relativehumidity of 100%) were supplied to the anode side and the cathode sideof the fuel cell, respectively. A back pressure was set to 0.1 MPa and acell temperature was set to 80° C. Then, an open circuit voltage (OCV)and a voltage in power generation at a current density of 0.2 A/cm²(0.2-A voltage) obtained under the above-mentioned conditions were eachmeasured.

In addition, the oxygen reduction activity was evaluated. That is, thecatalyst slurry was aspirated with a pipette and applied onto a diskelectrode (diameter: 5 mm) of a rotating ring-disk electrode apparatus(RRDE-1 SC-5 manufactured by Nikko Keisoku), followed by drying. Thus, aworking electrode was produced. In addition, a platinum electrode wasused as a ring electrode. 0.5 M sulfuric acid aqueous solution havingdissolved therein oxygen at normal temperature was used as anelectrolyte solution.

Next, the electrodes were rotated at a rotational speed of 1,500 rpm,and a current density during potential sweep at a sweep speed of 0.5mV/sec was recorded as a function of a potential. Then, from theresultant polarization curve, a voltage at which a reduction current of−10 μA/cm² flowed was recorded as an oxygen reduction-starting potential(E_(O2)) Further, the number of electrons involved in a reaction “n” wascalculated with the following equation; n=4I_(D)/(I_(D)+(I_(R)/N)). Inthis equation, I_(D) and I_(R) represent a disk current and a ringcurrent at a potential of 0 V, respectively. In addition, N representscollection efficiency. The collection efficiency was set to 0.372256.

FIG. 2 illustrates the results of evaluation of each of the carboncatalysts for its OCV (V), 0.2-A voltage (V), E_(O2) (V), and number ofelectrons involved in a reaction. As illustrated in FIG. 2, the powergeneration performance and oxygen reduction activity in the case ofusing any one of the carbon catalysts subjected to the metalimpregnation treatment (Examples 1 to 12) were improved compared tothose in the case of using any one of the carbon catalysts not subjectedto the metal impregnation treatment (Comparative Examples 1 and 2).

Further, the power generation performance and oxygen reduction activityin the case of using any one of the carbon catalysts subjected to theacid washing after the metal impregnation treatment (Examples 3 to 12)were improved compared to those in the case of using any one of thecarbon catalysts not subjected to the acid washing (Examples 1 and 2).In particular, the power generation performance in the case of using anyone of the carbon catalysts subjected to the additional metalimpregnation treatment using zirconium, titanium, or cerium (Examples 7to 9) was remarkably high. In addition, the power generation performancein the case of using the carbon catalyst into which nitrogen atoms hadbeen doped (Example 12) was also remarkably high.

In addition, the number of electrons involved in a reaction in the caseof using any one of the carbon catalysts not subjected to the metalimpregnation treatment (Comparative Examples 1 and 2) was 3.6. On theother hand, the number of electrons involved in a reaction in the caseof using any one of the carbon catalysts subjected to the metalimpregnation treatment (Examples 1 to 12) was 3.8 or 3.9, which waslarge.

[Evaluation by Temperature Programmed Desorption Method]

The carbon catalysts produced in Examples 3, 4, 7, 10, and 12 andComparative Example 1 above, and the ketjen black (KB) prepared inComparative Example 3 above, were each evaluated by a temperatureprogrammed desorption method. That is, a carbon catalyst was placed in atemperature programmed desorption apparatus (manufactured by BEL Japan,Inc.), the carbon catalyst was heated under such a high vacuum that acarrier gas (He) was caused to flow at 50 mL/min, and a desorbed gas wassubjected to measurement with a quadrupole mass spectrometer (QMS).

Specifically, first, the carbon catalyst was subjected to a pretreatment(desorption of a catalyst surface functional group by a heat treatment).That is, 0.02 g of the carbon catalyst was loaded into the centralportion of a reaction tube made of quartz, and then the tube was set inthe temperature programmed desorption apparatus. The temperature in theapparatus was increased to 50° C. at a rate of temperature increase of5° C./min and then held at the temperature for 40 minutes so that theapparatus was stabilized. After that, the carbon catalyst was subjectedto the heat treatment by heating the carbon catalyst to increase itstemperature to 900° C. at a rate of temperature increase of 10° C./min.Thus, the functional group on its surface was desorbed.

Next, the surface of the carbon catalyst was caused to adsorb oxygen.That is, first, the temperature in the apparatus was held at 150° C. for10 minutes so that the apparatus was stabilized. After that, an oxygen(O₂) gas was caused to flow through the carbon catalyst subjected to theheat treatment as described above so as to have a concentration of 5 vol%, and then the carbon catalyst was held at 150° C. for 20 minutes sothat the surface of the carbon catalyst (mainly an edge surface) wascaused to chemically adsorb oxygen.

Next, the carbon catalyst was subjected to a heat treatment, and thendesorbed carbon monoxide (CO) and carbon dioxide (CO₂) were subjected tomeasurement. That is, a helium (He) gas was made to flow in theapparatus at 150° C. for 25 minutes so that oxygen that had notchemically adsorbed was deaerated. Next, the temperature in theapparatus was increased from 150° C. to 900° C. at a rate of temperatureincrease of 10° C./min again. During the temperature increase, thehelium (He) gas was made to flow at 50 mL/min, carbon monoxide andcarbon dioxide produced by the desorption of an oxygen-containingcompound were detected, and a correlation between a temperature (axis ofabscissa) and a detected intensity (axis of ordinate) was recorded.

Then, the amounts of desorbed carbon monoxide and carbon dioxide weredetermined. That is, the integral values (detected intensity areas) ofthe detected intensities of carbon monoxide and carbon dioxide from 150°C., at which the heat treatment was initiated, to the temperature (400°C. or 900° C.) at which one wished to determine the amounts, were eachcalculated. Meanwhile, a calibration curve illustrating a correlationbetween the desorption amount of each of carbon monoxide and carbondioxide, and its detected intensity area was created by using apredetermined amount of calcium oxalate monohydrate (CaC₂O₄.H₂O) as areference substance. Specifically, the calibration curve was obtained bysubjecting 0.02 g of a sample, which was obtained by mixing alumina andcalcium oxalate monohydrate (CaC₂O₄.H₂O) so that the content of calciumoxalate was 250, 500, 750, or 1,000 μmol, to a heat treatment under theconditions described above. Then, the desorption amounts (releaseamounts) of carbon monoxide and carbon dioxide from the carbon catalystwere determined on the basis of the detected intensity areas obtained bythe measurement and the calibration curve.

FIG. 3 illustrates the results of evaluation of each of the carboncatalysts for its desorption amounts of carbon monoxide and carbondioxide in the temperature programmed desorption method from 150° C. to400° C. or 900° C. As illustrated in FIG. 3, the desorption amounts ineach of the carbon catalysts (Examples 3, 4, 7, 10, and 12) subjected tothe metal impregnation treatment were remarkably larger than those ineach of the carbon catalyst (Comparative Example 1) and the electricallyconductive carbon material (Comparative Example 3) not subjected to themetal impregnation treatment. That is, the metal impregnation treatmentremarkably increased the desorption amounts of carbon monoxide andcarbon dioxide in the temperature programmed desorption method.

The results show that the metal impregnation treatment increased theamount of the edge surfaces of carbon in the carbon catalyst, i.e.,increased its active surface area. Thus, the improvements in the powergeneration performance and oxygen reduction activity of the carboncatalyst through the metal impregnation treatment were considered to beprobably due to an increase in the amount of the edge surfaces (increasein the active surface area) as a result of the metal impregnationtreatment.

[Evaluation of Average La, Average Lc, and Average Number of Stacks]

The carbon catalysts produced in Examples 3, 4, and 10, and ComparativeExample 1, and the ketjen black (KB) prepared in Comparative Example 3,were each determined for its average crystallite sizes (average La andaverage Lc) and average number of stacks in a c-axis direction of acarbon network surface.

The average La, average Lc, and average number of stacks were calculatedby analysis of a powder X-ray diffraction pattern of the carbon catalystby a Diamond method. For this analysis, there was used software foranalysis (Carbon Analyzer D series, Hiroyuki Fujimoto,http://www.asahi-net.or.jp/˜qn6h-fjmt/) installed in a computer.

FIG. 4 illustrates the results of evaluation of each of the carboncatalysts for its average La, average Lc, and average number of stacks.As illustrated in FIG. 4, there was no marked difference in any of theaverage La, the average Lc, and the average number of stacks betweenExamples and Comparative Examples. That is, the average La, the averageLc, and the average number of stacks had no clear correlation with theimprovements in the power generation performance and the oxygenreduction activity.

In addition, the carbon catalysts subjected to the metal impregnationtreatment and the carbon catalysts not subjected to the metalimpregnation treatment each had its specific surface area determined bya nitrogen adsorption BET method. As a result, the specific surface areafell within the range of 450 m²/g or more and 650 m²/g or less in any ofthe carbon catalysts, and there was no marked difference between thecarbon catalysts.

In addition, the carbon catalysts subjected to the metal impregnationtreatment and the carbon catalysts not subjected to the metalimpregnation treatment were each evaluated for its crystallinity. As aresult, there was no marked difference between the carbon catalysts. Asdescribed above, the BET specific surface area and the crystallinityalso had no clear correlation with the improvements in the powergeneration performance and oxygen reduction activity through the metalimpregnation treatment.

[Evaluation of Oxygen Reduction Activity and Four-Electron ReductionReaction Rate in Air Cell]

First, a catalyst slurry containing any one of carbon materialsincluding the carbon catalysts produced in Examples 3 and 12 above, theketjen black prepared in Comparative Example 3, and the carbon materialcarrying platinum prepared in Comparative Example 4, was prepared. Thatis, 1 μL of a commercially available binder (SBR TRD-2001 manufacturedby JSR Corporation), 300 μL of ethanol, and 150 μL of distilled waterwere added to 5 mg of the carbon material, and the contents were mixedwith a mortar. The resultant mixture was ultrasonicated for 1 hour.Thus, a catalyst slurry was obtained.

Then, the oxygen reduction activity was evaluated. That is, the catalystslurry was aspirated with a pipette and applied onto a disk electrode(diameter: 5 mm) of a rotation ring-disk electrode apparatus (RRDE-1SC-5 manufactured by Nikko Keisoku), followed by drying. Thus, a workingelectrode was produced. In addition, a platinum electrode was used as aring electrode (counter electrode) and an Ag/AgCl electrode was used asa reference electrode. A 1 mol/dm³KOH aqueous solution having dissolvedtherein oxygen at normal temperature was used as an electrolytesolution.

Next, in the electrolyte solution, the electrodes were rotated at arotational speed of 1,500 rpm, the potential of the ring electrode wasset to 0.4 V, and a current density during potential sweep from 0.2 V to−0.5 V at a sweep speed of 0.5 mV/sec was recorded as a function of apotential.

Further, a four-electron reduction reaction rate E4 (%) was calculatedwith the following equation; E4={(I_(D)−I_(R)/N)}/{(I_(D)+I_(R)/N)}×100.In this equation, I_(D) and I_(R) represent a disk current and a ringcurrent at a potential of 0 V, respectively. In addition, N representscollection efficiency. The collection efficiency was set to 0.372256.

FIG. 5 illustrates the results of evaluation of the oxygen reductionactivity. In FIG. 5, the axis of abscissa indicates the potential (V vs.NHE) and the axis of ordinate indicates the current density (mA/cm²). Inaddition, FIG. 6 illustrates the results of evaluation of thefour-electron reduction reaction rate E4. In FIG. 6, the axis ofabscissa indicates the potential (V vs. NHE) and the axis of ordinateindicates the four-electron reduction reaction rate E4 (%). In FIG. 5and FIG. 6, the result in the case of using the carbon catalyst producedin Example 3 (PCoFeAW) is indicated by a solid line, the result in thecase of using the carbon catalyst produced in Example 12 (PCoFeAWNH₃) isindicated by a dashed line, the result in the case of using the ketjenblack (KB) prepared in Comparative Example 3 is indicated by achain-dashed line, and the result in the case of using the carbonmaterial carrying platinum (Pt/C) prepared in Comparative Example 4 isindicated by a chain double-dashed line.

As illustrated in FIG. 5, the carbon catalysts produced in Example 3 andExample 12 each exhibited an oxygen reduction activity that wasremarkably high compared to the ketjen black and was equivalent to thecarbon material carrying platinum.

In addition, as illustrated in FIG. 6, the four-electron reductionreaction rate E4 obtained in the case of using any one of the carboncatalysts produced in Example 3 and Example 12 was remarkably highcompared to that in the case of using the ketjen black, and wasequivalent to or higher than that in the case of using the carbonmaterial carrying platinum. In particular, the four-electron reductionreaction rate E4 obtained in the case of using the carbon catalystproduced in Example 3 was higher than that in the case of using thecarbon material carrying platinum in the potential range of 0 V to −0.5V.

The invention claimed is:
 1. A method of producing a carbon catalyst,comprising: a carbonization step of carbonizing raw materials containingan organic compound as a carbon source, a metal, and an electricallyconductive carbon material to produce a carbonized material; a metalimpregnation step of impregnating the carbonized material with a metal;and a heat treatment step of subjecting the carbonized materialimpregnated with the metal to a heat treatment.
 2. The method ofproducing a carbon catalyst according to claim 1, wherein the metalimpregnation step comprises impregnating the carbonized material with adifferent kind of metal from the metal in the raw materials.
 3. Themethod of producing a carbon catalyst according to claim 1, wherein theheat treatment step comprises heating the carbonized material at 400° C.or more.
 4. The method of producing a carbon catalyst according to claim2, wherein the heat treatment step comprises heating the carbonizedmaterial at 400° C. or more.
 5. The method of producing a carboncatalyst according to claim 1, wherein the metal in the metalimpregnation step is one or two or more kinds selected from the groupconsisting of titanium, chromium, manganese, iron, cobalt, nickel,copper, zinc, zirconium, niobium, molybdenum, lanthanum, cerium, andtantalum.
 6. The method of producing a carbon catalyst according toclaim 2, wherein the metal in the metal impregnation step is one or twoor more kinds selected from the group consisting of titanium, chromium,manganese, iron, cobalt, nickel, copper, zinc, zirconium, niobium,molybdenum, lanthanum, cerium, and tantalum.
 7. The method of producinga carbon catalyst according to claim 3, wherein the metal in the metalimpregnation step is one or two or more kinds selected from the groupconsisting of titanium, chromium, manganese, iron, cobalt, nickel,copper, zinc, zirconium, niobium, molybdenum, lanthanum, cerium, andtantalum.